Pacing apparatus and improved catheter

ABSTRACT

Improved apparatus and method for temporary or permanent pacing, comprising a catheter having a first pacing electrode positioned for placement in the patient&#39;&#39;s heart and a second pacing electrode positioned to be within the patient&#39;&#39;s body but sufficiently proximal that it is outside the patient&#39;&#39;s heart, the electrodes being connected through respective leads within the catheter to a Pacemaker (registered trademark, U.S. Patent Office) with the first electrode connected as the cathode. The Pacemaker may be external for temporary pacing, or implantable for permanent pacing.

United States Patent [191 Preston Oct. 28, 1975 PACING APPARATUS AND IMPROVED CATHETER [76] Inventor: Thomas A. Preston, 820 37th Ave.,

Seattle, Wash. 98122 22 Filed: Feb. 4, 1974 21 Appl. No.: 439,315

Related US. Application Data [63] Continuation-impart of Ser. No. 309,996, Nov. 28,

[52] US. Cl. 128/419 P; 128/404 [51] Int. Cl. A61N l/04 [58] Field of Search... 128/404, 418, 419 P, 419 R,

[56] References Cited UNITED STATES PATENTS 11/1969 Greatbatch 128/419 P 1/1974 Friedman 6/1974 Denniston 128/419 P OTHER PUBLICATIONS Rogel et al., Journal of Theracic & Cardiovascular Surgery, Vol. 61, No. 3, March, 1971, pp. 466-471.

Schwedel et al., Annals of the New York Academy of Sciences, Vol. 111, Art. 3, June 11, 1964, pp. 972-980.

Primary ExaminerWilliam E. Kamm Attorney, Agent, or FirmBenasutti and Preston [57] ABSTRACT 6 Claims, 6 Drawing Figures US. Patent Oct. 28, 1975 Sheet 10f2 3,915,174

\ /LEFT SUBCLAVIAN VEIN EXTERNAL JUGULAR VEINS RIGHT SUBCLAVIAN VElN SUPERIOR VENA CAVA RIGHT ATRIUM RIGHT VENTRICLE INTERIOR VENA CAVA ABOUT 6cm.

ABOUT 23 cm.

TO DISTAL E LECTRODE Fig. 2a

U.S. Patent Oct. 28, 1975 Sheet 2 of2 3,915,174

Fig 3 Fig. 4

PACING APPARATUS AND IMPROVED CATHETER CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part application of my copending application Ser. No. 309,996, filed Nov. 28, 1

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention lies in the area of heart pacing apparatus and, more particularly, in the area of catheters used with external and implanted Pacemakers for temporary and permanent pacing in a clincial environment. The apparatus and method of this invention are particularly adapted for demand pacing.

DESCRIPTION OF THE PRIOR ART Temporary pacing of a patient in the post-operative period following cardiac surgery is an established and effective means of treating arrhythmias or increasing cardiac output. Additionally, temporary pacing is particularly important and widely used with respect to complete heart block, especially in patients undergoing acute myocardial infarction. Such temperory pacing has been a widely used clinical procedure in this country for many years, and the technique of inserting the catheter into the patient and pacing from an external source is a common technique of cardiology. A number of instrument manufacturers produce clinically acceptable catheters, and there are several models of Pacemakers well known to cardiologists and suitable for carrying out this technique.

There have been two basic types of catheters available and in use for such external, or temporary pacing. A first type is what is referred to as a unipolar catheter, having one lead extending substantially the length of the catheter and being electrically connected to an electrode which is positioned inside the patients heart for transmitting the desired electrical signal thereto. This cardiac electrode is connected through the catheter lead to a first terminal of a Pacemaker device which, in temporary pacing, is external to the patient, and which is designed to produce a desired periodic pacing signal. The second terminal of the external Pacemaker is connected to an electrode which is generally clamped to the patients skin around or near the point of entry of the catheter, which may be approximately at the large vein opposite the patients right elbow. Another suitable site, such as in the femoral vein, may also be used for catheter insertion. Such electrode must be maintained in firm electrical contact with the patient, usually requiring some sort of electrically conductive paste be applied to the patients skin, as well as the use of additional means (such as suturing an electrode beneath the skin at the site of incision) for maintaining the electrode in firm position. The time required to attach the second electrode to the patients skin is considered, by most physicians, to be at best a considerable annoyance, and external electrodes attached to the skin are unreliable and require constant attention. When both the external electrode and the electrode which is placed in the patients heart are connected to the Pacemaker, the periodic output signals form the Pacemaker terminals produce bio-potentials in the patients heart of a character so as to induce stimulation of the heart, i.e., was to pace the heart.

The second type of standard catheter in common use, and clearly the preferred type, is what is referred to as a bipolar catheter, having both electrodes positioned near the distal end of the catheter, such that when the catheter is fully inserted into the patients heart, both electrodes are inside the heatt and in proper position to transmit the desired signal from the Pacemaker directly to the patients heart. The advantage of the bipolar catheter over the unipolar form is the obvious one of eliminating the requirement of making an external attachment of one electrode to the patients skin. Using the bipolar catheter, the two leads of the catheter are simply connected directly to the external Pacemaker, or to whatever device is in clinical use.

There are two basic reasons which lead to the conclu sion that the new and novel catheter design of this invention is not only advantageous but should be required for safe clinical use. The first of these concerns the phenomenon of induced ventricular arrhythmias associated with the use of artificial Pacemakers. The possibility of Pacemaker induced ventricular arrhythmias has been recognized for some time, but the extent of the clinical risk of such arrhythmias has not been known. In fact, research has shown that an electronic Pacemaker stimulus can cause a dangerous arrhythmia by falling during the vulnerable period of a preceding ventricular best. This possibility exists most commonly when an asynchronous artificial Pacemaker is in competition with normal sinus rhythm or ectopic beats from any source. The problem is particularly important in patients requiring pacing during acute myocardial infarction, as these patients are most susceptible to lifethreatening ventricular arrhythmias.

I have found evidence that ventricular arrhythmias are evoked by anodal stimulation, which evidence suggests that in the majority of instances an anode on or within the heart, of size and configuration to permit anodal stimulation, is necessary to produce ventricular tachycardia or ventricular fibrillation in humans with permanent or temporary pacing systems. All the available evidence points to the anode as the most common site or origin of Pacemaker induced ventricular fibrillation. Although commercially available Pacemakers have outputs which are probably too small to produce arrhythmias in normal human hearts, such units must be designed to produce stimuli exceeding the excitation thresholds of or more of all patients encountered. With time the excitation threshold for an implanted electrode system can rise to ten times the initial implantation threshold, and therefore Pacemakers are designed to deliver 10-30 times as great a stimulus as is required for effective pacing at the time of electrode implantation. Thus, under adverse conditions, such as acute myocardial infarction, etc., Pacemaker induced ventricular arrhythmias are possible, especially if the anode is positioned on or inside the ventricle.

As a result of the above conclusions, it is clear that only unipolar cathodal pacing should be used. As most pacing in a clinical situation is through temporary catheter electrodes, either a remote indifferent electrode (anode), or catheter with a distal pacing cathode and a large proximal anode, i.e., an anode at least ten times the surface area of the cathode, and positioned outside of the right ventricle, should be used. Since, as was dis cussed hereinabove, there is an overwhelming preference for a bipolar type of cathode which eliminates the requirement of attaching an electrode externally to the patients skin, there is a need for a catheter construction having a first (cardiac) electrode which is adapted to be positioned within the heart, and a second electrode positioned such that it will be within the patients body, but outside of and proximal to the heart and preferably of greater surface size than the cardiac electrode. Furthermore, the cardiac electrode should be used as the cathode, and the proximal electrode as the anode.

The second discovery which has led to my novel catheter apparatus design, and method for use of same, relates to the use of demand, or non-competitive Pacemakers. In the demand Pacemaker the pacing signal is generated only upon demand, i.e., when the natural pacing signal of the patient is not sensed. For ventricular pacing, such demand Pacemakers are commonly used to avoid competition with sinus or ectopic beats. Competition between artificial and natural Pacemakers can result in an unacceptable increase in heart rate and may precipitate serious ventricular arrhythmias. I have recently encountered samples of failure of proper demand function in the post-operative period resulting in either of these complications, and at each case the failure was due to a low voltage signal coming from the bipolar electrodes of the catheter in use, and normal demand function was restored by conversion to a unipolar system.

Although epicardial voltages in a bipolar system are usually well in excess of those required for demand function, in any heart bipolar electrodes can be positioned so as to detect a signal too small for demand sensing. A bipolar system adequate to detect sinus beats may not detect beats from a different origin such as ectopic ventricular beats. However, in every case that l have observed, regardless of the amplitude of the bipolar electrogram, a unipolar electrogram could be obtained which was greater in magnitude and sufficient for proper demand function. Conversion of a bipolar electrode system to a unipolar system, with only one electrode in the heart, results in a simple and effective means of increasing the signal detected by the Pacemaker.

Although the above discussion has related to a catheter designed for temporary pacing, there are also existing problems with presently used permanent pacing systems. Specifically, present art permanent systems generally use an arrangement as disclosed in the patent to Gretbatch, No. 3,478,746, wherein the housing of the Pacemaker unit itself comprises one electrode. This arrangement frequently causes muscle twitching around the housing electrode, which constitutes a substantial nuisance to the patient. Because of this, most surgeons avoid putting the Pacemaker housing underneath the muscle layer, but rather put it between the muscle and the skin. This too is undesirable from a surgical point of view, because it is easier for the Pacemaker housing to erode through the skin. Secondly, and potentially more serious, when an electrode is placed near a muscle it frequently picks up muscle potentials which interfere with proper demand sensing. For example, if the muscle in the vicinity of the housing electrode is voluntarily contracted, as in the use of arm or the shoulder, potentials from this muscle can be picked up by the electrode and relayed into the sensing mechanism. Thus, there is a need for a catheter adaptable for use with an implanted pacing unit which provides an electrode which is positioned safely outside of the heart but also a substantially great distance away from any muscle so that it does not, to any significant extent, pick up muscle potentials.

SUMMARY OF THE INVENTION It is the primary object of this invention to provide catheter apparatus for artificial pacing of a patients heart, which has the advantages of a bipolar electrode system in terms of ease of clinical use but which avoids the disadvantages of a bipolar electrode, and particularly which provides that the anode be outside of the patients heart, and which provides efficient pickup for demand pacing.

In accordance with the above object, there is pro vided catheter apparatus for pacing of a patients heart comprising a catheter having a first electrode, utilized as a cathode, positioned on the catheter such that it is within the patients heart when the catheter is fully positioned, and having a second electrode, utilized as an anode, and positioned proximal to the first electrode, having a surface area much larger than that of the cardiac electrode, and positioned so that it is external to the patients heart during the pacing operation. Pacing is achieved by periodically delivering the pacing signal between a cathode positioned within the heart and an anode positioned outside of the heart.

It is another object of this invention to provide an improved apparatus for pacing of a patient by which pacing signals are generated outside of the heart, transmitted within the patient through a catheter of improved design, and connected between a first pacing electrode positioned within the patients heart and a second pacing electrode positioned within the patient and outside of the patients heart.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatical sketch showing the placement of a catheter within a human body, and which indicates the critical areas of electrode placement according to this invention.

FIG. 2 is a sketch showing the catheter apparatus of this invention in combination with an artificial Pacemaker.

FIG. 2a is a detail sketch showing the connection of the anode of the catheter of this invention to one of the catheter electrical leads.

FIG. 2b is a detail sketch showing the connection of the cathode of the catheter of this invention to the other of the catheter leads.

FIG. 3 is a diagrammatic sketch showing the placement of an implantable Pacemaker and catheter within a human body, in accordance with this invention.

FIG. 4 is a sketch showing an alternate embodiment of the catheter apparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a diagrammatic sketch of a catheter 20 inserted into a human. Mostcommonly, the catheter is inserted at about position 21, into the right basilic vein. The tip of the catheter is manipulated through the superior vena cava, the right atrium, and into the right ventricle. The catheter may also be introduced through the external (or inter nal) jugular veins, subclavian veins, or femoral veins. At the end portion of the bipolar catheter external to the body a pair of electrical leads (or one lead for a unipolar) are connected to the Pacemaker for pacing. There are a number of commercially available Pacemakers which may used in the practice of this invention. Such Pacemakers, and their manner of use, are well known to cardiologists.

In a commonly used prior art bipolar catheter, the two electrodes are both caused to reside in the right ventricle, as shown at 24, 25. When a prior art unipolar catheter is utilized, there is only one heart electrode, such as 24, and a second electrode is placed upon the patients skin near the point of entry at 21. The same catheter apparatus is utilized for demand pacing.

Referring now to FIG. 2, there is shown a diagrammatic sketch of the catheter 30 utilized in the practice of this invention, connected to a Pacemaker 32. Pacemaker 32 may be either a conventional Pacemaker type device or a demand type Pacemaker device. The catheter is an elongated and flexible instrument, constructed preferably of a plastic material such as nylon or Teflon, and of generally tubular form with substantially constant outer diameter from end to end. The catheter of this invention has two electrical leads 34, 35, constructed of electrically conductive material, and embedded in the non-conductive plastic material. The larger of the two electrodes, 38, suitably a cylindrical ring, of conductive material, is positioned so that when the catheter is in place within the patient, it is outside of the patients heart. It is connected to a first of the catheter leads, 34, as shown in FIG. 2a, which in turn is connected to the positive terminal of Pacemaker 32, such that it is the anodal electrode. At the far distal end of the catheter, near the tip thereof, is an electrode 40, which also is suitably a ring of conductive material around the outside of the catheter, and in electrical contact with the other of the two conducting leads, 35, as shown in FIG. 2b. Lead 35 in turn is connected to the negative terminal of Pacemaker 32, such that electrode 40 is the cathodal electrode. This electrode is of relatively small surface area, and typically has a width of about 1-3 millimeters. For a catheter with outside circumference of approximately 6-10 millimeters, the total surface area would be approximately 6-24 square millimeters.

In accordance with the discussion hereinabove, and in order to achieve the purpose of avoiding anodal stimulation of the heart, it has been found that the second electrode, which is used as the anode, should be placed preferably at least 4 centimeters proximal to the heart (to the right atrium). This point is indicated in FIG. 1 by the dashed line indicated at 50. In addition, to accommodate the occurrences where the catheter may be introduced through the subclavian vein, the anode should not extend beyond the region indicated aproximately by the dashed line 52. For a typical human, the distance from the distal electrode (cathode) to dashed line 50 is about 23 centimeters, and the distance from dashed line 50 to dashed line 52 is about an additional 6 centimeters. Accordingly, the proximal electrode (anode) is suitably placed within this 6 centimeter distance (but need not be that long). For a catheter having an outside diameter of 2-3 millimeters, the surface of the anode should be about 100-300 square millimeters.

It is highly desirable that the proximal anode be much larger in surface area than the cathode, in order to distribute the anodal-induced, or positive-induced electric field intensity, so as not to stimulate surrounding structures. By making the anode at least about 10 times as large as the cathode in surface area, this is achieved.

In practice, the distal electrode of the catheter is made the cathode by connecting it to the negative terminal of the Pacemaker 32, and the proximal electrode is made the anode by connecting it, through lead 35, to the positive terminal of Pacemaker 32. It is seen that, in clinical use, the apparatus of this invention provides that the anode is positioned safely outside of the patients heart, and preferably at least 4 centimeters away form the patients heart, while the cathode is positioned within the patients right ventricle. By thus placing the anode outside of the heart, and in addition providing the anode with a surface area much larger than that of the cathode (so as to reduce electric field concentration around the anode) the possibility of anodal stimulation of the heart is effectively eliminated, and cathodal pacing is ensured. At the same time, however, the apparatus of this invention provides the advantages of the bipolar catheter, in that both electrodes are permanently affixed to the catheter, and there is no need for external placement of an electrode upon the patients skin. At the same time, the positioning of the electrodes in accordance with this invention provides an effection unipolar type of pickup from the heart, so that when the catheter apparatusof this invention is used with a demand Pacemaker, the danger of detection of less than threshold signals is substantially reduced.

It is to be understood that in order to ensure against anodal stimulation, it is desirable both to remove the anode from the vicinity of the heart and to make the surface area of the anode large. Although the design as shown in FIG. 2 is considered to be the best and safest design, it is to be understood that improvement over prior art forms of catheters may be achieved with various compromise designs. For example, if the anode were to extend into the heart, but had a large and extended surface area such as would be obtained if the anode were continuous almost to the point of entry, the distribution of the large anode surface would mitigate against anode stimulation. Similarly, simply positioning the anode outside of the heart, but making it of the same order of magnitude and surface size as the cathode, would achieve some improvement over the prior art. While the design criterion of positioning the anode at least four centimeters external to the heart is a critical limitation necessary to ensure a factor of safety against anodal stimulation, placement of the anode within less than four centimeters of the heart would still be an improvement over the prior art in accordance with the principles of this invention. Similarly, the design criterion of making the anode at least 10 times as great as the cathode is also a critical limitation necessary to ensure against anodal stimulation, but use of an anode of lesser size would still be within the broad scope of this invention.

In addition to the aforementioned use of my novel catheter for temporary pacing, it may also be used as an improved permanent, or implantable catheter with an implanted pacing system. Referring now to FIG. 3, there is shown a permanent Pacemaker 101 implanted within the patient. For implantation in the region as shown, a single incision is made as indicated roughly by line 103 to open the cephalic vein for insertion of the catheter, and to implant the Pacemaker unit. The catheter 102 is inserted through one of the cephalic veins, or may be inserted into the subclavian vein, and thence into the patients heart. An electrode 106, which is utilized as a cathode, is placed at the tip end of the catheter, and electrode 105, used as the anode, is placed sufficiently proximal thereto so that it is outside of the patients heart when the cathode is positioned within the right ventricle. The construction of the catheter is the same as described hereinabove, with the exception that the total length of the catheter is less (within the range of about 58 85 centimeters) so that it can be implanted under the skin. Alternately, the Pacemaker may be implanted as shown at 108, with the catheter 109 placed into the external jugular vein. This procedure, used infrequently, requires two incisions, one in the neck (to get to the jugular), and the other to bury the power unit. The catheter is tunneled beneath the skin from the point of the Pacemaker unit 108 to the incision at the jugular vein. Thus, the catheter as employed in permanent implantation can be inserted on either the right or the left side of the patient.

For this sort of permanent catheter, there is a particular need to provide means such that the two leads are inserted into the power unit (Pacemaker) such that there can only be a proper connection of the Pacemaker output to the respective anode and cathode electrodes. In other words, the connection means is such that the distal electrode is always connected to the cathode (negative) terminal of the Pacemaker and the remote (proximal) electrode is always connected to the anode (positive) terminal of the Pacemaker. Such means may be provided by a conventional keying arrangement.

It is to be further noted that for permanent implantation catheters, as well as the temporary catheters described hereinabove, the necessary distance between the distal electrode and the remote electrode, in order to achieve the desired anodal pacing of the heart, will vary with the actual patient. My observations have determined that for a typical patient, as noted hereinbefore, the distance from the cathode to the anode must be about 19 cm in order that the anode is out of the heart when the cathode is inserted into the ventricle. However, by definition, some patients will be smaller than typical patients, and accordingly this distance can be less than 19 cm for smaller patients. I have determined that for such smaller patients, the proximal electrode (anode) may be placed 17 cm from the distal electrode (cathode) and still be safely outside of the patients heart when the distal electrode is fully positioned within the patients right ventricle.

As illustrated in FIG. 4, the catheter 120 (same as catheter 102) may have a distal electrode 121 (which is positioned within the ventricle) and a proximal electrode 122 which is positioned a distance L from the distal electrode. For the small patient, L may be 17 cm, at which distance electrode 122 would be positioned safely outside of the heart. The distance L may, of course, be greater than 17 cm, and preferably should be within 29 cm, as set forth above. The important feature is that electrode 122 be such a distance from electrode 121 so as to provide means for pacing between a first position within the right ventricle and a second position outside of the heart and inside the body.

In order to insure that the proximal electrode does not cause muscle twitching, or sense muscle potentials, it must be positioned safely in the circulatory system. This is accomplished by placing the proximal electrode within 29 cm from the distal electrode.

The basic electrode configuration of my catheter design as discussed hereinabove is adaptable for use with other catheter embodiments, specifically embodiments incorporating at least one additional electrode utilized for sensing. Referring again to FIG. 4, there is shown a diagram of a catheter embodiment comprising a distal electrode (cathode) 121, a remote electrode (anode) 122, and a sensing electrode 124 which is placed sufficiently close to electrode 121 so that both electrodes 121 and 124 may be positioned in the heart. This embodiment may be utilized where, for example, there is a need for sensing of the QRS signal produced by a pacer stimulus. Because of the large polarization afterpotential from the pacing stimulus, there is a need for an extra electrode within the heart (124 in this embodiment) which is displaced from the pacing electrode 121, such that it can sense the QRS signal. Pacing is from 121 to 122, and sensing is between 124 and 122. Electrode 122, which is larger than electrode 121, can be used for both pacing and sensing because it has a larger surface area and therefore less polarization afterpotential. The embodiment shown in FIG. 4 provides this capability, as well as providing the capability of pacing the patient cathodally between a cathode positioned in the heart and an anode positioned within the body but outside of the heart. For this use, sensing electrode 124 is positioned about l-2 cm from the distal electrode, (but could be up to 6-8 cm from the distal electrode).

A similar catheter such as that illustrated in FIG. 4 may be utilized for atrial-synchronized ventricular pacing, where the sensing electrode 124 is positioned on the catheter such that when the distal pacing electrode is positioned in the right ventricle the sensing electrode is positioned in the right atrium. This permits sensing atrial excitation between the sensing electrode (124) and the proximal electrode (anode 122), and pacing the patient (in response to said sensed atrial signal) from between the distal pacing electrode (cathode 121) and the proximal electrode (anode 122). For this use, the sensing electrode may be typically placed about 10-15 cm proximal from the distal electrode.

I claim:

1. Implantable pacing system apparatus, comprising:

a. a pacing circuit adapted to be implanted in a human patient;

b. a catheter adapted for insertion through a portion of the patients circulatory system into the heart, said catheter having a first pacing electrode at a first end and a second pacing electrode positioned at least a distance of 17 cm from said first electrode, said catheter having electrical leads each connecting to a respective one of said electrodes;

c. signal connecting means for connecting said pacing circuit to said electrical leads at said catheters other end so that the pacing signals generated by said pacing circuit are connected to said pacing electrodes with the first pacing electrode being the cathode and the second pacing electrode being the anode; and

(1. whereby when said pacing circuit is implanted in a patient and said catheter is inserted so that said first pacing electrode is in the patients heart and said second pacing electrode is outside of the patients heart and within the patients circulatory system, said system provides cathodal pacing of the patient.

2. The pacing system apparatus as described in claim 1, wherein said second pacing electrode is positioned 17-29 cm from said first pacing electrode.

3. A catheter adapted for insertion through a patients circulatory system into the patients heart, for use in cardiac pacing, including demand pacing, of the patient, comprising:

a. an elongated flexible catheter having two conducting leads extending through respective lengths thereof;

b. a distal pacing electrode positioned near a first end of said catheter, and connected electrically to a first of said leads; and

c. a proximal pacing electrode positioned on said catheter at a distance of at least about 17 cm from said distal electrode and connected electrically to the second of said leads.

4. The apparatus as described in claim 3, wherein said proximal pacing electrode is positioned within a range of about 17-29 cm from said distal electrode.

5. The catheter as described in claim 3 in combination with a pacing generator for generating pacing signals, and with connecting means for connecting said pacing generator to said catheter leads so that said pacing signals are operatively connected between said pacing electrodes such that said distal electrode is the cathode and said proximal electrode is the anode.

6. Catheter apparatus adapted to be positioned in a patient for use in cardiac pacing of the patient, with a predetermined end extending into the patients heart, comprising:

a. an elongated flexible catheter having three conducting leads;

b. a distal pacing electrode positioned on said catheter near said predetermined end thereof, and connected electrically to a first of said leads;

c. a proximal pacing electrode positioned on said catheter at a distance at least about 17 cm from said distal electrode, and connected electrically to a second of said leads; and

d. a sensing electrode positioned within the range of ll5 cm proximal to said distal electrode and connected electrically to the third of said leads.

"H050 UNI'I'I'II) STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 1 ,174 Dated October 28, 1975 Invcntor(s) Thomas A. Preston It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

.Column 1, line 14, delete "clincial" and substitute clinical--;

line 24, delete "temperory" and substitute temporary-. Column 2, line 6, delete "heatt" and substitute heart-;

line 27, de' lete "best" and substitute beat.

.Column 5, line 3, after "may", insert be-. Column 6, line 11, de]l ete "form" and substitute --from;

line 24, del'ete "effection" and substitute -effective.

Signed and Sealed this third Day of February 1976 [SEAL] I Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner uj'Patenrs and Trademarks Disclaimer 3,915,174.Th0mas A. Preston, Seattle, Wash. FACING APPARATUS AND IMPROVED CATHETER. Patent dated Oct. 28, 1975. Disclaimer filed Jan. 5, 1977, by the inventor. Hereby enters this disclaimer to the term subsequent to July 8, 1992.

[Oflicial Gazette March 8, 1977.]

29 33 UNITED STATES lA'll'lNT om-lcm CERTIFICATE OF CORRECTION Patent No. ,174 Dated October 28, 1975 Inventor(s) Thomas A. Preston It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

ri v Column 1, line 14, delete "clincial" and substitute clinical-;

line 24, delete "temperory" and substitute -temporary. Column 2, line 6, delete "heatt" and substitute heart-;

line 27, delete "best" and substitute --beat-. .Column 5, line 3, after "may", insert. be-.

Column 6, line 11, dellete "form" and substitute from;

line 24, delete "effection" and substitute effective-.

Signed and Sealed this third Day of February 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting ff (mnmissiuner ofPatents and Trademarks 

1. Implantable pacing system apparatus, comprising: a. a pacing circuit adapted to be implanted in a human patient; b. a catheter adapted for insertion through a portion of the patient''s circulatory system into the heart, said catheter having a first pacing electrode at a first end and a second pacing electrode positioned at least a distance of 17 cm from said first electrode, said catheter having electrical leads each connecting to a respective one of said electrodes; c. signal connecting means for connecting said pacing circuit to said electrical leads at said catheter''s other end so that the pacing signals generated by said pacing circuit are connected to said pacing electrodes with the first pacing electrode being the cathode and the second pacing electrode being the anode; and d. whereby when said pacing circuit is implanted in a patient and said catheter is inserted so that said first pacing electrode is in the patient''s heart and said second pacing electrode is outside of the patient''s heart and within the patient''s circulatory system, said system provides cathodal pacing of the patient.
 2. The pacing system apparatus as described in claim 1, wherein said second pacing electrode is positioned 17-29 cm from said first pacing electrode.
 3. A catheter adapted for insertion through a patient''s circulatory system into the patient''s heart, for use in cardiac pacing, including demand pacing, of the patient, comprising: a. an elongated flexible catheter having two conducting leads extending through respective lengths thereof; b. a distal pacing electrode positioned near a first end of said catheter, and connected electrically to a first of said leads; and c. a proximal pacing electrode positioned on said catheter at a distance of at least about 17 cm from said distal electrode and connected electrically to the second of said leads.
 4. The apparatus as described in claim 3, wherein said proximal pacing electrode is positioned within a range of about 17-29 cm from said distal electrode.
 5. The catheter as described in claim 3 in combination with a pacing generator for generating pacing signals, and with connecting means for connecting said pacing generator to said catheter leads so that said pacing signals are operatively connected between said pacing electrodes such that said distal electrode is the cathode and said proximal electrode is the anode.
 6. Catheter apparatus adapted to be positioned in a patient for use in cardiac pacing of the patient, with a predetermined end extending into the patient''s heart, comprising: a. an elongated flexible catheter having three conducting leads; b. a distal pacing electrode positioned on said catheter near said predetermined end thereof, and connected electrically to a first of said leads; c. a proximal pacing electrode positioned on said catheter at a distance at least about 17 cm from said distal electrode, and connected electrically to a second of said leads; and d. a sensing electrode positioned within the range of 1-15 cm proximal to said distal electrode and connected electrically to the third of said leads. 